1. Field of the Invention
This invention relates to optical fibers, and more particularly to lenses for the distribution and delivery of light emerging from an optical fiber.
2. Prior Art
Lenses are often applied in the medical field to focus light, typically from a laser source, onto a treatment site. When fiber optics are employed, microlenses are used as the focusing device due to their size and availability. The microlens is attached to the treatment end of the optical fiber to distribute the light from the fiber into a desired pattern or intensity distribution. For applications requiring insertion of the treatment end into the body such as photodynamic therapy (PDT), laser angioplasty, laser lithotripsy, laser surgery, etc., a svelte, low profile delivery device is needed. The device must be safe, easily inserted into the body, capable of delivering substantial power and produce a desired output.
Optically transmissive fibers for transmitting light energy to a remote location from a source are well known in the surgical literature. For example, Sottini, et al., in U.S. Pat. No. 4,842,390, describe a fiber optic device for transmission of laser energy into a blood vessel for angioplasty. Such lenses are useful for either focusing or diverging the light as it emanates from the tip of the optical fiber. Goldenberg, in U.S. Pat. No. 4,641,912 uses a focusing tip on an optical fiber which receives its input light from an excimer laser for producing a high intensity, ultrathin beam of light. All such medically useful optical fibers normally comprise a fiber element having a proximal end and a distal or treatment end. The optical fiber element is adapted to conduct radiation, usually from lasers, from the proximal end of the optical fiber to be emitted at the distal or treatment end. It may also include a microlens secured to the distal end of the optical fiber.
Aita, et al., in U.S. Pat. No. 5,093,877 describe a treatment fiber having a convex lens placed at the treatment end of an optical fiber. The lens is positioned to receive laser radiation emitted from the distal end of the optical fiber and focus it on a treatment site. The lens has two surfaces: a first surface adjacent to, but separated from the distal end of the optical fiber to receive laser radiation from the optical fiber; and a second surface which is substantially convex, positioned to distribute the laser light. The first lens surface is shaped to provide a predetermined distribution pattern from the second lens surface. The assembly, which may be called a microlens also includes a tubular sleeve coupled to the first lens surface. The tubular sleeve is crimped to the optical fiber to hold the distal tip of the fiber core at the focal point of the lens.
While these devices are adequate for some applications, improvements in the design would facilitate the clinical procedures while improving the safety and clinical results. When used internally the potential exists for the lens mounting structure to fail and become detached leaving pieces of the device in the human body.
In summary, the prior art optical fibers for medical treatment utilizing microlenses on the end of an optical fiber have the following shortcomings:
1. They rely on a crimping procedure to secure the lens mounting device to the fiber optic jacket; PA0 2. They produce an output which is not perfectly focused because the crimping procedure distorts the mounting device and therefore its ability to hold the fiber optic and the lens in position relative to each other; PA0 3. They don't have the capacity to handle high-power applications; PA0 4. They couple light out of the fiber inefficiently; and, PA0 5. They do not provide a barrier for biological fluids such as blood. Such fluids can enter the microlens cavity and reduce the efficiency of the microlens.